The Standard Industrial Classification (SIC) was a system for classifying industries by a four-digit code as a method of standardizing industry classification for statistical purposes across agencies. Established in the United States in 1937, it is used by government agencies to classify industry areas. Similar SIC systems are also used by agencies in other countries, e.g., by the United Kingdom's Companies House.

In the United States, the SIC system was last revised in 1987 and was last used by the Census Bureau for the 1992 Economic Census, and has been replaced by the North American Industry Classification System (NAICS code), which was released in 1997. Some U.S. government departments and agencies, such as the U.S. Securities and Exchange Commission (SEC), continued to use SIC codes through at least 2019.

The SIC code for an establishment, that is, a unique business with a registered U.S. headquarters, was determined by the industry appropriate for the overall largest product lines of the company or organization of which the establishment was a part. The later NAICS classification system has a different concept, assigning establishments into categories based on each one's output.